By Doug Bright
ASX-listed Red Metal’s innovative “metallurgy-first” approach to defining the potential of its unique rare earths discovery in Queensland has paid early dividends, with recent testing showing extraction levels up to 90 per cent on two key elements that are used in the lucrative electric vehicle (EV) market – neodymium and praseodymium.
The testwork also showed maximum extractions of the rarer heavy rare earths, dysprosium and terbium, of 60 per cent and 64 per cent, respectively. Both dysprosium and terbium are typically only mined in serious quantities in China and both are also crucial ingredients in the manufacturing of industrial magnets that are a key part of an EV engine.
The Sydney-based company now believes Sybella represents a potentially new deposit style for Australia – and possibly the world – with its rare earths hosted by partly weathered and fresh granite extending through a 12km-by-3km area.
Traditional sources of rare earths are usually found in either a hard rock carbonatite setting or in clay-hosted deposits and Red Metal says its Sybella project is somewhere in between. It says Sybella could potentially be as easy to extract as the clay-hosted deposits, but without the handling and filtration complexities that come with processing large volumes of clay ore.
‘The metallurgical results have far exceeded our expectations and underline the potential for heap leachable REO ore at Sybella.’Red Metal managing director Rob Rutherford
Recent outstanding results from leaching testwork have strengthened the $42m-capped company’s arm and are something of a proof-of-concept for the unique, granite-hosted rare earths geology.
The company’s defined target area is about 20km south-west of Australia’s renowned Mt Isa mining centre and city.
Red Metal managing director Rob Rutherford said; “The metallurgical results have far exceeded our expectations and underline the potential for heap leachable REO ore at Sybella. The Sybella results, as received to date, have been reviewed against peer projects using publicly available leach data and can be compared favourably to the recent exciting Brazilian discoveries. The metallurgical work shows opportunities to enhance these recovery results and Red Metal will accelerate its exploration programs. Red Metal is confident that a highly competitive project could be developed with low capital and low operating costs.”
Clay-hosted rare earths can experience processing and handling issues while typical hard-rock carbonatite deposits require more complex processing such as fine comminution by grinding, screening, gravity separation, flotation and high-temperature cracking of mineral concentrates. Sybella’s rare earths oxides, however, exist as weak acid soluble fluoro-carbonate minerals evenly distributed as disseminations and micro-fracture infillings throughout the low-acid consuming host granite.
At Sybella, rare earth fluoro-carbonates in the weathered host granite start right from surface and the rock can range from almost friable to easily broken under mild pressures. The company says it could be amenable to simple ripping or digging by an excavator within the upper 10m to 15m and even as deep as 20m.
Red Metal’s testwork shows excellent rare earth oxide recoveries can be achieved from both weathered and fresh rock with low acid consumption and importantly, the leach extracted low levels of impurities.
Surprisingly, and contrary to most operations, Sybella recoveries are actually reduced by the excessive grinding that simply exposes more of the barren host rock to the leachant, which creates other negative metallurgical issues and wastes acid.
To put it in layman’s terms, the metallurgy shows that the less you mess with Sybella, the more forthcoming it will be, pointing to coarse crushing and simple, low-cost heap or dump leach processing as the optimal way forward for the project’s likely ore type.
In addition to the solid extraction numbers, the recent testing at Sybella also showed a low average sulphuric acid consumption of just 37kg per tonne – a key cost input in any mining operation. The minimum was 23kg per tonne, accompanied by only low extractions of aluminium and iron impurities at 7 and 22 per cent, respectively.
Importantly, recoveries of the potentially serious deleterious components, thorium and uranium, have been low at 20 grams per tonne and 1g/t, respectively.
While the latest tests were undertaken up to a maximum of 96 hours, the recovery curves indicate that the longer residence times that are more typical of dump leaches – which can be days, weeks or even months – will likely yield even better recoveries.
Further recovery and cost reduction improvements look like they will be forthcoming with increasing particle size, residence time and careful tweaking of the pH (acidity),
The company says it is already undertaking a second phase of metallurgy test work to explore comminution characteristics, leach recoveries on varying size fractions from crushed core samples and it will run trials to remove impurities.
Planning for further drilling is also underway, likely to be on a broad grid of 800m-by-400m to scope out the extent of the potential resource to gain a sense of the rare earths grade and continuity along strike and into the deeper weathered zones and relatively fresh rock.
Red Metal’s Sybella prospect has an air of anticipation about it, of something new and potentially lucrative, nonetheless it may take a little while for punters to fully understand how its characteristics and metallurgy set it apart from the more traditional clay-hosted and hard rock rare earths discoveries.
And while metallurgy tests are not always sexy, they are nonetheless critical to understanding the economic potential of a rare earths project as poor metallurgy can kill a project overnight.
That Red Metal appears to have jumped this hurdle even before tabling a maiden resource should put to bed the question around processing – at least at this early stage.
It will now be fascinating to see the numbers in any future prefeasibility study on Sybella. They just might rewrite the traditional rare earths production cost curve.
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Source: Thanks smh.com